Rubber articles made from natural or synthetic rubber include surgeons gloves, physicians examining gloves, workers gloves, prophylactics, catheters, balloons, tubing, sheeting and the like. Some articles, in particular, gloves, require the ability of donning i.e. the ability of the rubber article to be slid on and off skin (tissue) surfaces without undue clinging or friction. Surgeons gloves require wet donning, i.e., the ability to be slid over wet skin surfaces, while physicians examining and workers gloves require the ability to be slid over dry skin surfaces. Other rubber articles, like catheters and tubing, require some means to isolate the rubber from body fluids and tissue.
While this invention pertains to polymeric coatings for all rubber articles, it will focus on gloves, which are the most complex of rubber articles in terms of use and manufacture. To achieve acceptable donning properties, the rubber surface of a glove which comes in contact with skin or tissue has to be modified to reduce friction.
Surgeons gloves, as of today, require the donning surface to be sufficiently hydrophilic in order to absorb moisture that may be present on the surface of skin or tissue when the article is donned. Hydrogel coatings as described, for instance, in U.S. Pat. No. 3,813,695, incorporated herein by reference, have been employed to achieve this property.
Examination and other gloves, by contrast, do not have a hydrophilicity requirement but still require the ability of the rubber article to be slid over skin (tissue) surfaces with minimal drag or friction.
Traditionally, this has been achieved by applying talc or other powdered materials, such as modified corn starch, over the skin or tissue contacting surface. Talc can no longer be used, and other powders can contaminate the field of work. The same applies for gloves used by workers in dust-free environments such as in the manufacture of computer chips and other electronic articles.
With reference to FIG. 1, the conventional way of manufacturing rubber gloves has been to dip a mold or former in the shape of the article to be formed in a coagulant slurry containing calcium nitrate and calcium carbonate. After drying, the mold is immersed in a rubber emulsion (latex) for a time sufficient for the rubber to coagulate and form a coating of desired thickness. The formed coagulated rubber article is oven cured, cooled, and then dipped into a starch slurry. The starch coated surface is dried to provide a powder coat. After cooling, the rubber article is stripped from the mold. This turns the glove inside out. The mold is cleaned and recycled.
Water leaching may be, and usually is, employed as part of the procedure to remove rubber impurities.
The methods and materials of glove manufacture are also described, for instance, in U.S. Pat. Nos. 3,411,982 and 3,286,011 to Kavalier et al., both incorporated herein by reference, "Polyurethane Latexes for Coagulation Dipping," Sadowski et al., Elastomerics, August 1979, pp. 17-20, incorporated herein by reference, and in "Dipping with Natural Rubber Latex," Pendle et al., Natural Rubber Technical Bulletin, also incorporated herein by reference.
Halogenation, e.g. chlorination, and other chemical surface treatments have been used to eliminate the need for a powder coat on the final product to enable dry donning. While effective, this step is expensive and has the shortcoming of reducing shelf life of the rubber article. It would be desirable to provide a rubber article with a powder-free donning surface without resorting to the expensive and article-deteriorating practices now in vogue. This could substantially reduce the cost of manufacture and maximize the shelf life of the rubber article.
U.S. Pat. No. 4,302,852 to Joung, incorporated herein by reference, proposed to covalently bond an RTV silicone coating to the interior surface of a rubber surgeons glove after formation of the glove. This is stated to reduce but not eliminate the need for a donning powder.
U.S. Pat. No. 4,304,008, also to Joung and incorporated herein by reference, applies a covalently bonded silicone or urethane to the outer surface of the glove and halogenates the inner surface. The halogenated inner surface eliminates the need for a donning powder.
U.S. Pat. No. 4,310,928, also to Joung and incorporated herein by reference, teaches the deposition of a lipo compound (lipid or lipophilic substances) in place of a powder of mineral origin in combination with a surfactant in a coagulant solution to form a uniform film on a glove mold onto which the rubber is coagulated. The lipo compound and surfactant enable stripping of a formed glove from its mold.
These and other proposals have not achieved commercial acceptance.